Recently, for example, in rear monitors of vehicles, a technique has been known by which an image captured with a fisheye camera having a wide view of angle and large distortion is coordinate-converted so as to correct image distortion and obtain an image easy to see for users (e.g., refer to Japanese Patent Application Laid-open No. 2009-177703).
In general, sensors, such as image sensors capturing images, have widened dynamic ranges while output systems, such as displays outputting the captured images, have narrow dynamic ranges. As for a color depth represented by the number of output bits per pixel, a sensor has a 12-bit color depth while an output system has an 8-bit color depth, for example.
Under such circumstances, when a captured image that includes outdoor and indoor areas or shady and sunny areas and has a wide dynamic range is output by an output system, underexposed (blocked up shadows) and overexposed (blown out highlights) areas occur. In order to address the problem, a dynamic range compression technique by which a dynamic range of a captured image is compressed according to characteristics of an output system is disclosed in Japanese Patents No. 4161719 and No. 4214457.
In general, the dynamic range compression is carried out in a succeeding stage (just before an output to an output system) to image processing because the dynamic range compression is carried out according to the characteristics of the output system and the number of bits capable of being handled in various image processes needs to be increased. Hence, when the above-described coordinate conversion and dynamic range compression are carried out, the coordinate conversion is first carried out and followed by the dynamic range compression.
However, when the coordinate conversion and the dynamic range compression are carried out in this order, ringing or artifacts occur in an image that has been subjected to dynamic range compression due to an effect of an enlargement rate of an image that has been coordinate-converted. As a result, image quality deteriorates.